RF surgical devices have been widely used for removing the tumors or the pathological tissues. One of the features of the RF surgical devices is less invasive due to the particular use of the devices such that the devices are inserted into the specific region of the pathological tumors or the tissues which are close to the pathological tumors. The RF surgical devices induce the heat in the tumors or the pathological tissues which suffer the pathology or cancers in a manner that the RF power is absorbed in the right tissue regions which suffer the pathology so that the tissue regions cauterized by the thermal heating. The treatment by the RF surgical devices is percutaneous but less laparotomy and therefore the treat is less invasive so that the patient can be discharged from the hospital in a short time.
There are two categories of RF surgical devices. The first one is an RF ablation device that can make an induced current flow in the tissue to which the device is inserted and then the tissue is coagulated by the thermal heat generated by the induced current flow. This has been proposed by LeVeen as described in the reference 1. The second category is an RF surgical device that radiates microwave power which is absorbed by the water included in the tissue to which the RF surgical device is inserted. The power absorption in the cell water heats the tissue up above the temperature at which protein of the tissue decomposes and the cells of the tissue die. The microwave frequency as 945 MHz or 2.45 GHz has been used. The therapy that uses such RF surgical device is called RF hyperthermia oncology or percutaneous microwave coagulation.
A therapeutic product called as “Microtaze” (a trade mark of “ ” Alfresa Pharma, Co. Ltd., Ref. 1) is well-known. This product exploits the above two therapeutic effects. The electric probe (abbreviated as “probe”, hereinafter) used for Microtaze has a coaxial structure similar to coaxial cables. More specifically, as illustrated in FIG. 1 and FIG. 2, it consists of a central conducting wire 102 (abbreviated as “a central conductor”), a cylindrical dielectric insulator 103 therearound, an outer conducting cylinder 104 (as abbreviated as “an outer conductor”) and a jacket 105 covering thereof. The outer conductor 104 is formed into an electrode and the central conductor 102 the other electrode. For the purpose of easy surgical operation, the tip of the probe is formed into a needle tip as illustrated in FIG. 1 and FIG. 2 or a bullet head 106 in FIG. 3 and FIG. 4. The overall structures are called a thermo-therapeutic probe, especially, thermo-therapeutic monopole probe (abbreviated as a TTMP) in accordance with the electrical characteristics of this electric probe.
A new thermo-therapeutic probe, which is dedicated for heating by microwave absorption in the water, has been announced in addition to the thermo-therapeutic probe described in the above second category (Ref. 2). The probe is made from a semi-rigid coaxial cable of which coaxial structure is formed for the purpose thereof. More concretely, as illustrated in FIG. 5 and FIG. 6, the outer conductor 104 is segregated into certain segments between which an electrically isolating gap 107 is made for every two adjacent segments. A first electrode 108 which is a part of the outer conductor 104 and one of the adjacent segments is connected to the central conductor 102 is formed for the outer conductor 104. A second electrode 109 which is the other part of the outer conductor 104 and the other adjacent segments and which is isolated from the first electrode 108 is formed from the outer conductor 104. The outer conductor is covered by a jacket 105. Accordingly, the electrodes of this thermo-therapeutic probe have a structure of an antenna assembly, especially, a dipole antenna. The whole antenna assembly is covered by an insulating material or put into an insulating case made of insulating material. This structure is called thermo-therapeutic dipole probe (abbreviated as a TTDP, hereinafter).
An insulating case 117 or 117A of the TTDP described in Ref. 1, as illustrated in FIG. 5 and FIG. 6, is made of hard polyvinyl chloride (or PVC) or polytetrafluoroethylene (or PTFE). The insulating case 117 covers the whole part of the dipole antenna and insulating case 117A encloses the whole part of the dipole antenna therein. Another part of the structure of the outer conductor, in which the part of the first electrode is electrically connected to the central conductor by means of disc conductive piece 110, so that cylindrical symmetry is realized for the probe structure, is known. Such TTDPs are illustrated in FIGS. 7 and 8, which are particularly covered by the insulating case 117.
By comparing the therapeutic effects obtained by the TTMP and the TTDP, the actual phenomenon of the usage shows that the pathological tissue into which the TTMP is inserted is heated in the region in a manner that the region between the central conductor and the surrounding outer conductor near by is heated by the electric induction current flowing thereof (FIG. 9). Therefore the cauterized (heated but not burned) region by the TTMP is localized in the distance form the central conductor 102 (which is at t0) to r1. On the other hand, the first electrode and the second one of the TTDP construct a dipole antenna The water of the pathological tissue region which surrounds the position where the TTDP is inserted absorbs the microwave radiated from such position and is heated to be higher than the temperature at which the protein of the pathological tissue decomposes. Therefore the “cauterized” region cured by the TTDP is larger than that by TTMP (as illustrated in FIG. 10) due to the physical property of microwave radiation which is horizontal microwave propagation after converted from the TEM mode existing in the coaxial cable from which the dipole antenna comprising the first and the second electrodes is formed. The cauterized region is from r=ts which is the surface of the insulating case 117 or 117A to r=r2. Especially, tumors such as cancer tissues easily become necrotic in such low temperature as slightly higher than the protein decomposition one. Therefore the TTDP can provide very little burden against sound tissues but cauterize tumors to become necrotic. This is the same therapeutic effect against tumors as that of hyperthermia oncology. The detailed structures of the TTMP and the TTDP illustrated in FIG. 11 and FIG. 12 are same as those illustrated in FIG. 2 and FIG. 6, respectively.